Expression pattern of two related cystic fibrosis-associated calcium-binding proteins in normal and abnormal tissues

Abstract

This paper reports further study of the identity and function of a protein shown to be elevated in serum from cystic fibrosis (CF) patients and clinically normal heterozygotes. Monoclonal antibodies, specifically recognizing the tentatively named cystic fibrosis antigen (CFAg), were produced. Immunoaffinity purification of CFAg from several sources revealed two components: 11×103 and 14×103Mr proteins. cDNA clones corresponding to each protein have been isolated. Data-base comparisons of the deduced amino acid sequences suggest that both genes encode related but distinct calcium-binding proteins. We propose the name calgranulin A and B, for the 11×103 and 14×103Mr components, respectively. It is clear from the assignment of the calgranulin genes to chromosome 1 that neither is the product of the mutant CF gene, which maps to chromosome 7. We have used the monoclonal antibodies to study the tissue distribution of the two proteins in a wideranging immunohistological survey. Where possible the pattern of expression was confirmed by RNA blot analysis. Strong calgranulin expression in granulocytes was confirmed. In addition to myeloid cells, a restricted subset of normal stratified squamous epithelia were found to be calgranulin-positive. These included tongue, oesophagus and buccal cells, the last of which has been shown to have altered calmodulin activity in CF patients. Using indirect alkaline phosphatase staining, tissue sections of lung, pancreas and skin (normally considered sites where the CF defect is expressed) were not calgranulin-positive. However, by indirect immunofluorescence, nasal polyp sections showed weak patchy calgranulin expression in some epithelial cells, and stronger, higher frequency expression when such cells were briefly cultured. A number of hyperproliferative, neoplastic or frankly malignant epithelia were found to express the two proteins. Calgranulin expression is a good marker for ‘reactive’ epithelium in skin and for squamous cell carcinomas of skin, lung and buccal tissues. The calgranulin-positive permanent cell line from a buccal squamous cell carcinoma may prove a suitable tool for unravelling the calgranu-lin-CF relationship.